Integrating Google Map Tiles with Cesium

I have a few questions regarding integrating Google Map 2D tiles with Cesium:

  1. Can Google Map tiles only be used if one has a Google Earth Enterprise Server?
  2. Are there legal restrictions for using Google Map tiles with Cesium, and is this integration recommended?

Although I have found these two threads but want to understand more about it. Links of thread Thread 1 and Thread 2.